Encoder preference and when to change it EN

Leave it on Auto unless you have a reason. Here is what a reason looks like.

Encoder preference sets the video format Rekorder uses for new recordings. Leave it on Auto (recommended) unless you have a specific reason to change it. Auto picks the best supported format on your computer.

Where to find it

Open the Rekorder extension popup and go to its settings. See Extension settings, tab by tab if you need help finding them.
Open the Video tab.
Use the Encoder preference menu.

The new choice applies to recordings you start afterwards. It doesn't change recordings you've already made.

The options

Auto (recommended): Rekorder checks which formats your browser can encode and picks the best one. If your computer has a hardware encoder for a format, Auto prefers it. A hardware encoder does the video encoding on your graphics hardware instead of your processor, which leaves the processor free for everything else. If there isn't one, Auto uses WebM.
WEBM: Records in WebM.
MP4: Records in MP4.
MP4 (WebRTC): Records in MP4 using a different recording method. It needs a short calibration the first time. See below.

Under the menu, a Used codec line shows the exact format your next recording will use. It says "browser default" if Rekorder has no specific format to name.

When changing it makes sense

Auto already avoids the usual problems, so change it only when you have a reason. For example:

You want a specific format, such as MP4 or WebM, for your recordings.
Your recordings stutter or your computer struggles while recording, and you want to test whether another format runs better on your machine.

When you choose WEBM or MP4 yourself, Rekorder uses that format even if the other one would be hardware accelerated. Auto weighs hardware support. A manual choice doesn't.

If you change it to try to fix a problem and it doesn't help, set it back to Auto.

If your computer can't encode a format

The preference follows your account to your other computers. Each computer uses it only if it can encode that format. Otherwise it falls back to the best format it does have.

Options your computer can't use are greyed out and labelled "(not supported)". The choice stays visible so you can see what your account is set to.

MP4 (WebRTC) and calibration

MP4 (WebRTC) is only available if your browser supports it. When you select it, Rekorder calibrates by measuring your computer's audio and video timing. This takes a few seconds and happens automatically.

A tab opens in front of your others and closes on its own when the measurement is done. Leave it alone until it closes.
While calibration runs, Start is unavailable. If you start a recording before it has finished, Rekorder holds off starting it and runs calibration first.
If calibration fails, a message says "MP4 (WebRTC) not supported." and the setting switches to MP4.
To try again after a failure, select MP4 (WebRTC) again. Each time you select it, Rekorder retries the calibration.

How MP4 (WebRTC) differs from MP4

For someone watching, the two look the same. Both produce an .mp4 file with H.264 video. The differences are in how the file is made and in the audio format. MP4 (WebRTC) exists because it can use hardware H.264 encoding more reliably, so it may run faster on a low-end computer.

Downloads:

Offline recordings: The format matters. Rekorder saves the file from your browser's storage exactly as recorded, with nothing converted. An MP4 (WebRTC) recording downloads as a fragmented MP4 (a file written in small pieces as it records) with Opus audio.
Cloud recordings: The format doesn't matter. Rekorder's servers process the uploaded recording before you download it.

Editing: The format makes no difference. Editing happens after the recording has been converted.